1. Field of the Invention
The present invention relates to a ceramic laminated capacitor and, more particularly, to an approximately cylindrical ceramic laminated capacitor which is suitable for automatic mounting.
2. Description of the Prior Art
Ceramic laminated capacitors were developed in order to obtain small-sized and large-capacity capacitors. Generally, they have an external appearance shown in FIG. 11. Such a ceramic laminated capacitor is externally composed of a ceramic dielectric 1 and outer electrodes 2, to which are connected the end portions of an inner electrode (not shown) which is arranged in the shape of the teeth of a comb in the interior of the ceramic dielectric 1.
A method of manufacturing a ceramic laminated capacitor having the above-described structure will now be explained.
A slurry is first formed by milling ceramic powder, a binder resin of, for example, acryl or polyvinyl, and a solvent such as water or trichloroethane in a predetermined ratio, and a green sheet is formed of the slurry in the step of casting. In the step of casting, the slurry is applied to a continuous base film having a certain degree of heat resistance and release properties such as a polyethylene terephthalate film to a thickness of 20 to 100 .mu.m, and thereafter the solvent in the slurry is dried to form what is called a green sheet, which is then released from the base film.
A predetermined shape was blanked out of the green sheet, and an electrode paste containing palladium and the like is printed on the green sheet in the next step of printing to form a multiplicity of inner electrodes.
A plurality of such green sheets are laminated such that the directions of the inner electrodes on the adjacent green sheets are opposite. In the subsequent step of press bonding, the laminated green sheets are press bonded so that the adjacent green sheets are integrally bonded. Thus a laminate of the green sheets is obtained.
The laminate is cut at each electrode with, for example, a blade in the next step of cutting, whereby a multiplicity of chips are obtained from one laminate. The chip is baked in the next step to remove the binder resin, and is further baked to sinter the ceramic powder in the slurry. In the subsequent step of abrasion, the corner portions including the sections are abraded by barrel finishing.
A metal-glazed conductive paste is bonded to both ends of the chip to form outer electrodes, which are then subjected to nickel-plating or solder-plating, whereby a ceramic laminated capacitor having a configuration of a rectangular parallelepiped such as that shown in FIG. 11 is formed.
Such a laminated ceramic is formed by cutting the laminate of green sheets, as described above, so that the basic external appearance thereof is in the shape of a rectangular parallelepiped, as shown in FIG. 11. Generally, a multiplicity of laminated ceramic capacitors are accommodated in a continuous belt-like body A called a taping reel. When they are actually handled, the belt-like body A is conveyed by a reel machine, and the laminated ceramic capacitors accommodated in the belt-like body A are sucked due by means of vacuum pressure successively so that they are automatically mounted on a printed circuit base board at predetermined positions.
An automatic mounting machine which conveys capacitors at a high speed by utilizing vibration has recently been developed in place of the above-described taping reel system. Such an automatic mounting machine conveys a multiplicity of chips successively by vibrating a synthetic resin tube which accommodates the chips. According to this machine, since chips are conveyed by vibration, it is possible not only to increase the speed at which the chips are conveyed but also to improve the efficiency at which the chips are accommodated in comparison with the taping reel system. Since it is necessary to make the chips being conveyed slide smoothly in the tube, this machine is suitable for chips having a cylindrical external configuration, for example, cylindrical single-layer ceramic capacitors having a smaller capacity than the above-described ceramic laminated capacitor. On the other hand, ceramic laminated capacitors having a rectangular parallelepipedic external configuration are inconveniently caught in the tube, so that it is difficult to convey them smoothly.
To solve this problem, methods of producing an approximately cylindrical ceramic laminated capacitor from a rectangular parallelepipedic chip by chamfering the outer peripheral corners of the rectangular parallelepipedic chip in the step of grinding or cutting before or after the step of baking have recently been proposed (Japanese Patent Laid-Open No. 34622/1984, Japanese Patent Laid-Open No. 82712/1984). However, such chamfering process is very difficult for small-sized chips. Chamfering a chip before the step of baking involves a risk of inducing the displacement of the inner electrode or separation between the green sheet layers, while chamfering a chip after the step of baking takes much time because the chip after being baked is very hard.